Cellulose from Pinus radiata sawdust was utilized to obtain cellulose xanthates used as matrixes in controlled release formulations of simazine (6-chloro-N2,N4-diethyl-1,3,5-triazine-2,4-diamine)and trifluraline (2,6 dinitro- N, N-dipropyl-4-trifluoromethylaniline) herbicides. Cellulose was extracted from sawdust using ethanolic solution acidified with nitric acid, obtaining a 35% of yield. The xanthate matrixes were prepared suspending cellulose, sodium hydroxide and carbon disulfide to obtain xanthates with sulfur incorporation ranging between 700-2800 mgkg-1 of xanthate. Then three xanthate matrixes were selected to encapsulate the herbicides by addition of hydrogen peroxide. Formulations selected with minor content of sulfur did not show any control in the release of herbicides. The other two selected formulations showed a further control of release to both herbicides and were very similar between them. At the beginning these formulations released over 50-60% of the herbicides, but after ten days they release under 1% daily. The characteristics showed by these formulations could minimize the adsorption of these herbicides in soils, but they require a further development to be evaluated under field conditions